Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A mixing apparatus comprising: a) a mixing well characterized by an
internal volume not exceeding 100 ml.; b) a drive mechanism including a
stationary circumferential gear on an inner surface of the mixing well;
and c) a planetary mixing element driven by a mixing element gear which
engages the stationary circumferential gear.

Claims:

1. A mixing apparatus, the apparatus comprising:a) a mixing well
characterized by an internal volume not exceeding 100 ml.;b) a drive
mechanism including a stationary circumferential gear on an inner surface
of the mixing well; andc) a planetary mixing element driven by a mixing
element gear which engages the stationary circumferential gear.

2. Apparatus according to claim 1, wherein the drive mechanism is adapted
to provide sufficient shear force to mix a mixture characterized by a
viscosity of at least 500 Pascal/second.

3. Apparatus according to claim 2, wherein the viscosity of at least 500
Pascal/second is achieved within 90 seconds of an onset of mixing.

4. Apparatus according to claim 1, comprising:d) a cover engageable by the
mixing well and adapted for closure thereof.

5. Apparatus according to claim 4, wherein the cover includes a locking
ring.

6. Apparatus according to claim 1, wherein the drive mechanism is adapted
for manual operation.

7. Apparatus according to claim 1, comprising:d) a wiping element adapted
to concurrently engage an inner surface of the mixing well and the
planetary mixing element.

8. Apparatus according to claim 1, comprising:d) a central mixing element
positioned substantially at a center of the mixing well.

9. Apparatus according to claim 8, comprising:e) a wiping element adapted
to concurrently engage an inner surface of the mixing well, the planetary
mixing element and the central mixing element.

10. Apparatus according to claim 8, wherein the central mixing element
rotates about its own axis.

11. Apparatus according to claim 10, wherein the central mixing element
and the planetary mixing element rotate in opposite directions.

12. A mixing apparatus, the apparatus comprising:a) a mixing well
characterized by an internal volume not exceeding 100 ml.;b) a drive
mechanism adapted to operate at least one mixing element positioned in
the mixing well; andc) a wiping element adapted to engage an inner
surface of the mixing well and including at least one wiping aperture
substantially conforming to the at least one mixing element;wherein the
wiping element does not interfere with operation of the drive mechanism;
andwherein the withdrawal of the at least one mixing element from the
mixing well causes the at least one wiping aperture to remove at least a
portion of the mixture from the at least one mixing element.

13. Apparatus according to claim 12, wherein the wiping element rotates
within the mixing well while engaging an inner surface thereof.

14. Apparatus according to claim 12, wherein the drive mechanism is
adapted to provide sufficient shear force to mix a mixture characterized
by a viscosity of at least 500 Pascal/second.

15. Apparatus according to claim 12, comprising:d) a cover engageable by
the mixing well and adapted for closure thereof.

16. Apparatus according to claim 15, wherein the cover includes a locking
ring.

17. Apparatus according to claim 14, wherein the viscosity of at least 500
Pascal/second is achieved within 90 seconds of an onset of mixing.

18. Apparatus according to claim 12, wherein the wiping element is adapted
to remove an adherent portion of a mixture characterized by a viscosity
of at least 500 Pascal/second from the at least one mixing element.

19. Apparatus according to claim 18, wherein the at least one mixing
element includes at least two mixing elements.

20. Apparatus according to claim 12, wherein the drive mechanism is
adapted for manual operation.

21. A mixing apparatus, the apparatus comprising:a) a mixing well
characterized by an internal volume not exceeding 100 ml.;b) a central
mixing element deployed substantially at a center of the mixing well;c)
at least one planetary mixing element which revolves around the central
mixing element;wherein a first distance (d1) between the central
mixing element and the planetary mixing element is substantially
equivalent to a second distance (d2) between the planetary mixing
element and an inner surface of the mixing well.

22. Apparatus according to claim 21, wherein the planetary mixing element
is adapted for manual operation.

23. Apparatus according to claim 21, wherein the planetary mixing element
and central mixing element are adapted to provide sufficient shear force
to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

24. A drive mechanism for a mixing apparatus, the drive mechanism
comprising;a) a set of teeth defining a circular path on an inner
circumference of a vessel characterized by an internal volume not
exceeding 100 ml;b) a toothed wheel characterized by an axis, the wheel
adapted to engage said set of teeth and to rotate about the axis; andc)
an actuator adapted to provide a force which causes the toothed wheel to
advance along the circular path.

25. A mechanism according to claim 24, comprisingd) a drive transfer
element connecting between the axis of the toothed wheel and a second
wheel positioned substantially at a center of the circular path.

26. A mechanism according to claim 25, wherein provision of a force
through the actuator causes the drive transfer element to rotate the
second wheel about an axis through the center of the circular path.

27. A mechanism according to claim 24, wherein the toothed wheel drives a
planetary mixing element.

28. A mechanism according to claim 25, wherein the second wheel drives a
central mixing element.

29. A mechanism according to claim 24, wherein the actuator is manually
powered.

30. A mechanism according to claim 24, adapted to provide sufficient shear
force to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

31. A method of mixing components of a viscous mixture, the method
comprising:a) placing the components in a mixing well characterized by an
inner volume of not more than 100 ml;b) deploying at least one planetary
mixing element and a central mixing element in the mixing well; andc)
operating a manual drive mechanism to cause the planetary mixing element
to both rotate about its own axis and revolve around the central mixing
element in order to mix the components to form a mixture.

32. A method according to claim 31, comprising:e) engaging a wiping
element to at least one of the mixing elements such that withdrawal of
the mixing element from the mixing well causes the wiping element to wipe
mixture from the mixing element.

33. A method according to claim 31, wherein the drive mechanism is adapted
to provide sufficient shear force to mix a mixture characterized by a
viscosity of at least 500 Pascal/second.

34. A method according to claim 33, wherein the viscosity of at least 500
Pascal/second is achieved within 90 seconds of an onset of mixing.

35. A method according to claim 31, wherein the manual drive mechanism
supplies a sufficient force to cause the planetary mixing element to move
through a mixture characterized by a viscosity of at least 500
Pascal-second.

36. An apparatus for transferring a viscous material, the apparatus
comprising:a) a first container capable of containing a viscous
material;b) a transfer piston insertable in the first container so that
the piston forms a circumferential seal with respect to the container,
the transfer piston including a hole; andc) a mechanism for attaching an
aperture of a second container to the hole in the transfer piston;wherein
insertion of the transfer piston into the first container causes the
viscous material to pass through the aperture into the second container.

37. Apparatus according to claim 36, adapted to provide sufficient force
to cause a viscous material characterized by a viscosity of at least 500
Pascal/second to flow through the aperture of the second container.

38. Apparatus according to claim 37, configured so that manual
manipulation of the first container and the transfer piston produces the
sufficient force.

39. Apparatus according to claim 36, wherein the transfer piston is
adapted to remove at least a portion of the viscous material from a
mixing element as the mixing element is removed from the first container.

40. A method of mixing components of a viscous mixture, the method
comprising:a) placing the components in a mixing well characterized by an
inner volume of not more than 100 ml;b) operating a drive mechanism to
cause mixing of the material in the inner volume during a period when the
viscosity is at least 500 Pascal/sec.

41. A method according to claim 40, comprising driving a planetary mixing
element by means of the drive mechanism.

Description:

RELATED APPLICATIONS

[0001]The present application claims the benefit under 119(e) of U.S.
provisional patent applications U.S. 60/738,556, filed on Nov. 22, 2005,
U.S. 60/762,789, filed on Jan. 26, 2006; and U.S. 60/765,484, filed on
Feb. 2, 2006 all of which are entitled "METHODS, MATERIALS AND APPARATUS
FOR TREATING BONE AND OTHER TISSUE".

[0002]The present application is also a continuation in part of U.S.
patent application Ser. No. 11/360,251 entitled "METHODS, MATERIALS AND
APPARATUS FOR TREATING BONE AND OTHER TISSUE", filed on Feb. 22, 2006.

FIELD OF THE INVENTION

[0003]The present invention relates to mixing apparatus and to methods of
mixing.

BACKGROUND OF THE INVENTION

[0004]Mechanical mixers for mixing components to homogeneity are well
known. Their applications include, but are not limited to, baking,
building construction and medicine.

[0005]Mixing apparatus for high viscosity mixtures must be adapted to
provide sufficient shear force to continue moving against great
resistance. In some cases, the resistance increases during mixing because
the viscosity of the mixture increases.

[0006]One example of a case where the viscosity of the mixture increases
during mixing is preparation of a polymer/monomer mixture. When a polymer
and monomer are combined, a polymerization reaction begins. The
polymerization reaction increases the average polymer chain length in the
mixture and/or causes cross-linking between polymer chains. Increased
polymer chain length and/or cross linking between polymer chains
contribute to increased viscosity

[0007]Polymerization mixtures are often employed in formulation of bone
cement. One common polymer/monomer pair employed in bone cement
formulation is polymethylmethacrylate/methylmethacrylate (PMMA/MMA).
Because PMMA/MMA bone cements typically set to a solid form, reaction
conditions for the polymerization reaction are generally adjusted so that
mixing PMMA and MMA produces a liquid phase which lasts several minutes.
This is typically achieved by mixing a monomer liquid including MMA and,
optionally DMPT and/or HQ, with a polymer powder including PMMA and,
optionally Barium Sulfate and/or BPO and/or styrene. As a result,
previously available mixing equipment is constructed for use with a
liquid polymerization mixture and is not well suited to mixing of highly
viscous cements that have substantially no liquid phase during mixing.

[0008]The following references are cited as being generally indicative of
mixer types which are currently available for use in preparation of bone
cement. The list does not purport to be exhaustive.

[0009]U.S. Pat. No. 5,302,020; US 2003/0174576; U.S. Pat. No. 6,994,465
and U.S. Pat. No. 4,961,647 disclose use of a central mixing element in
combination with a planetary mixing element which revolves around the
central mixing element. The disclosure of each of these patents is fully
incorporated herein by reference.

[0010]U.S. Pat. No. 5,415,474 and U.S. Pat. No. 7,029,163 disclose a
transfer mechanism as part of a mixing apparatus. The disclosure of each
of these patents is fully incorporated herein by reference.

[0011]U.S. Pat. No. 5,549,381 discloses a wiper which removes adhering
mixture from a ribbon configuration mixing element as the mixing element
is removed from the mixing apparatus. The disclosure of this patent is
fully incorporated herein by reference.

SUMMARY OF THE INVENTION

[0012]A broad aspect of some embodiments of the present invention relates
to mixing of highly viscous materials in small batches. In an exemplary
embodiment of the invention, "highly viscous" indicates a viscosity of
500, 700 or 900 Pascal/second or lesser or greater or intermediate
viscosities. Exemplary means of determining viscosity are set forth in
Krause et al. (1982) "The viscosity of acrylic bone cements", Journal of
Biomedical Materials Research, 16:219-243) which is fully incorporated
herein by reference. Optionally, this viscosity is achieved within 30,
60, or 90 seconds of onset of mixing. However, under some circumstances
the mixing may take a longer time. A small batch may be 100, 50, 25, 15
or 5 ml or lesser or intermediate volumes at the completion of mixing.

[0013]In an exemplary embodiment of the invention, the highly viscous
material is a bone filler or "bone cement". Optionally, the bone cement
includes a polymeric material, for example polymethylmethacrylate (PMMA).
Optionally, the bone cement is of a type described in one or more of U.S.
patent applications U.S. 60/738,556; U.S. 60/762,789; 60/765,484 and Ser.
No. 11/360,251. The disclosures of these applications are fully
incorporated herein by reference.

[0014]An aspect of some embodiments of the present invention relates to a
mixer for a small batch of a highly viscous material including a drive
mechanism employing a stationary circumferential gear on an inner surface
of a mixing well. In an exemplary embodiment of the invention, the
stationary circumferential gear drives a planetary mixing element. The
planetary mixing element travels circumferentially around the mixing well
while rotating with respect to its own axis.

[0015]In an exemplary embodiment of the invention, the planetary mixing
element mixes the material in conjunction with a central mixing element.
In an exemplary embodiment of the invention, the central mixing element
is positioned substantially in a center of a mixing well. Optionally, the
central mixing element and/or the planetary mixing element rotate on
their own axes.

[0016]In an exemplary embodiment of the invention, rotation of the
planetary mixing element and the central mixing element is characterized
by different radial velocities with respect to their respective axes.

[0017]In an exemplary embodiment of the invention, rotation of the
planetary mixing element and the central mixing element is in opposite
directions on their respective axes.

[0018]An aspect of some embodiments of the present invention relates to a
mixer for a small batch of viscous material including at least one
planetary mixing element which revolves around a central mixing element
deployed substantially at a center of the mixing well, wherein a distance
(d) between outer surfaces of the mixing elements and between the
planetary mixing element and an inner wall of the mixing well is
substantially equivalent.

[0019]An aspect of some embodiments of the present invention relates to a
mixer for a small batch of viscous material characterized by a gear ratio
between a stationary circumferential gear and a gear of a planetary
mixing element selected to produce a desired shearing force on a mixture.

[0020]An aspect of some embodiments of the present invention relates to a
mixer for a small batch of viscous material characterized by mixing
elements of a size selected to produce a desired shearing force on a
mixture.

[0021]In an exemplary embodiment of the invention, for a desired shear
force, the selected gear ratio increases as (d) increases. In an
exemplary embodiment of the invention, for a desired shear force, the
selected gear ratio increases as a diameter of a mixing well increases.

[0022]An aspect of some embodiments of the present invention relates to a
method of mixing components of a small batch of a mixture with a
viscosity of at least 500 Pascal/second including operating a manual
drive mechanism to cause a planetary mixing element to rotate about its
own axis and to revolve around a central mixing element.

[0023]An aspect of some embodiments of the present invention relates to
use of a wiping element to automatically separate a viscous material from
at least one mixing element of a mixing apparatus as the mixing element
is removed from the apparatus so that the viscous material is retained in
the apparatus. In an exemplary embodiment of the invention, the wiping
element includes at least one wiping aperture which substantially
conforms to a mixing element. Optionally, the wiping aperture is round,
optionally substantially circular. In an exemplary embodiment of the
invention, the wiping element revolves within the mixing well during
operation of the drive mechanism.

[0024]An aspect of some embodiments of the present invention relates to an
apparatus for transferring a viscous material from a first container to a
second container. In an exemplary embodiment of the invention, the
apparatus is adapted for use with bone cement. Optionally, the first
container is a mixing well and the second container is a portion of an
injection apparatus. In an exemplary embodiment of the invention, manual
manipulation of components of the apparatus produces sufficient force to
cause a material characterized by a viscosity of 500 Pascal/sec to flow
through an aperture between the first container and the second container.

[0025]According to various embodiments of the invention, a desired shear
force for a small batch of viscous material may be produced by varying
one or more of:

[0026]a) roughness of surfaces in a mixing well and/or on mixing elements,
to create a boundary layer;

[0048]In an exemplary embodiment of the invention, there is provided a
mixing apparatus, the apparatus includes:

[0049]a) a mixing well characterized by an internal volume not exceeding
100 ml.;

[0050]b) a drive mechanism adapted to operate at least one mixing element
positioned in the mixing well; and

[0051]c) a wiping element adapted to engage an inner surface of the mixing
well and including at least one wiping aperture substantially conforming
to the at least one mixing element;

[0052]wherein the wiping element does not interfere with operation of the
drive mechanism; and

[0053]wherein the withdrawal of the at least one mixing element from the
mixing well causes the at least one wiping aperture to remove at least a
portion of the mixture from the at least one mixing element.

[0054]Optionally, the wiping element rotates within the mixing well while
engaging an inner surface thereof.

[0055]Optionally, the drive mechanism is adapted to provide sufficient
shear force to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

[0056]Optionally, the apparatus includes:

[0057]d) a cover engageable by the mixing well and adapted for closure
thereof.

[0058]Optionally, the cover includes a locking ring.

[0059]Optionally, the viscosity of at least 500 Pascal/second is achieved
within 90 seconds of an onset of mixing.

[0060]Optionally, the wiping element is adapted to remove an adherent
portion of a mixture characterized by a viscosity of at least 500
Pascal/second from the at least one mixing element.

[0061]Optionally, the at least one mixing element includes at least two
mixing elements.

[0062]Optionally, the drive mechanism is adapted for manual operation.

[0063]In an exemplary embodiment of the invention, there is provided a
mixing apparatus, the apparatus includes:

[0064]a) a mixing well characterized by an internal volume not exceeding
100 ml.;

[0065]b) a central mixing element deployed substantially at a center of
the mixing well;

[0066]c) at least one planetary mixing element which revolves around the
central mixing element;

[0067]wherein a first distance (d1) between the central mixing
element and the planetary mixing element is substantially equivalent to a
second distance (d2) between the planetary mixing element and an
inner surface of the mixing well.

[0068]Optionally, the drive mechanism is adapted for manual operation.

[0069]Optionally, the drive mechanism is adapted to provide sufficient
shear force to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

[0070]In an exemplary embodiment of the invention, there is provided a
drive mechanism for a mixing apparatus, the drive mechanism includes;

[0071]a) a set of teeth defining a circular path on an inner circumference
of a vessel characterized by an internal volume not exceeding 100 ml;

[0072]b) a toothed wheel characterized by an axis, the wheel adapted to
engage said set of teeth and to rotate about the axis; and

[0073]c) an actuator adapted to provide a force which causes the toothed
wheel to advance along the circular path.

[0074]Optionally, the mechanism includes

[0075]d) a drive transfer element connecting between the axis of the
toothed wheel and a second wheel positioned substantially at a center of
the circular path.

[0076]Optionally, provision of a force through the actuator causes the
drive transfer element to rotate the second wheel about an axis through
the center of the circular path.

[0080]Optionally, the mechanism is adapted to provide sufficient shear
force to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

[0081]In an exemplary embodiment of the invention, there is provided a
method of mixing components of a viscous mixture, the method includes:

[0082]a) placing the components in a mixing well characterized by an inner
volume of not more than 100 ml;

[0083]b) deploying at least one planetary mixing element and a central
mixing element in the mixing well; and

[0084]c) operating a manual drive mechanism to cause the planetary mixing
element to both rotate about its own axis and revolve around the central
mixing element in order to mix the components to form a mixture.

[0085]Optionally, the method includes:

[0086]e) engaging a wiping element to at least one of the mixing elements
such that withdrawal of the mixing element from the mixing well causes
the wiping element to wipe mixture from the mixing element.

[0087]Optionally, the drive mechanism is adapted to provide sufficient
shear force to mix a mixture characterized by a viscosity of at least 500
Pascal/second.

[0088]Optionally, the viscosity of at least 500 Pascal/second is achieved
within 90 seconds of an onset of mixing.

[0089]Optionally, the manual drive mechanism supplies a sufficient force
to cause the planetary mixing element to move through a mixture
characterized by a viscosity of at least 500 Pascal-second.

[0090]In an exemplary embodiment of the invention, there is provided an
apparatus for transferring a viscous material, the apparatus includes:

[0091]a) a first container capable of containing a viscous material;

[0092]b) a transfer piston insertable in the first container so that the
piston forms a circumferential seal with respect to the container, the
transfer piston including a hole; and

[0093]c) a mechanism for attaching an aperture of a second container to
the hole in the transfer piston;

[0094]wherein insertion of the transfer piston into the first container
causes the viscous material to pass through the aperture into the second
container.

[0095]Optionally, the apparatus is adapted to provide sufficient force to
cause a viscous material characterized by a viscosity of at least 500
Pascal/second to flow through the aperture of the second container.

[0096]Optionally, the apparatus is configured so that manual manipulation
of the first container and the transfer piston produces the sufficient
force.

[0097]Optionally, the transfer piston is adapted to remove at least a
portion of the viscous material from a mixing element as the mixing
element is removed from the first container.

[0098]In an exemplary embodiment of the invention, there is provided a
method of mixing components of a viscous mixture, the method includes:

[0099]a) placing the components in a mixing well characterized by an inner
volume of not more than 100 ml;

[0100]b) operating a drive mechanism to cause mixing of the material in
the inner volume during a period when the viscosity is at least 500
Pascal/sec.

[0101]Optionally, the method includes driving a planetary mixing element
by means of the drive mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0102]Exemplary non-limiting embodiments of the invention described in the
following description, read with reference to the figures attached
hereto. In the figures, identical and similar structures, elements or
parts thereof that appear in more than one figure are generally labeled
with the same or similar references in the figures in which they appear.
Dimensions of components and features shown in the figures are chosen
primarily for convenience and clarity of presentation and are not
necessarily to scale. The attached figures are:

[0103]FIG. 1 is a simplified flow diagram illustrating an exemplary
sequence of events associated with use of a mixing apparatus according to
exemplary embodiments of the invention;

[0104]FIG. 2 is a perspective view of an exemplary mixing apparatus with
the mixing elements removed from the mixing well;

[0106]FIGS. 4A and 4B are a schematic representation and an engineering
projection showing rotation direction and distances for an exemplary
drive mechanism respectively;

[0107]FIG. 5 is a diagram illustrating shear stress gradients between a
planetary mixing element and a central mixing element according to
exemplary embodiments of the invention;

[0108]FIGS. 6, 7 and 8 illustrate an exemplary wiping element adapted for
use with an exemplary mixing apparatus; and

[0109]FIGS. 9 and 10 illustrate a transfer module adapted for use with
exemplary mixing apparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Overview

[0110]U.S. application 60/738,556; U.S. 60/762,789; U.S. 60/765,484; and
Ser. No. 11/360,251 (hereinafter "the inventor's previous applications"),
the disclosures of which are each fully incorporated herein by reference,
disclose polymeric bone cement formulations which are characterized by a
rapid transition to a high viscosity state. According to exemplary cement
formulations disclosed in these applications, mixture of monomer and
polymer components produces a mixture characterized by a viscosity in the
range of 400 to 500 Pascal/second substantially as soon as the polymer is
wetted by the monomer. In practice, this can take as little as 30
seconds.

[0111]Previously available bone cement formulations were characterized by
a relatively long liquid phase and a short working window during which
the cement was suitable for injection. A new class of cement
formulations, disclosed in the inventor's previous applications is
characterized by a rapid transition to a high viscosity without a
persistent liquid phase followed by a relatively long working window
before the cement sets to solidity. The almost immediate transition to
high viscosity of the new class of cement formulations disclosed in the
inventor's previous applications means that high shear forces are
desirable in order to assure complete mixing. For this new class of
cement formulations, it is not feasible to mix components when the
mixture is still in the liquid state because there is essentially no
liquid state.

[0113]Exemplary mixing apparatus according to the present invention may
also be employed with conventional bone cement formulations. Optionally,
exemplary mixing apparatus according to the present invention may be
employed after the polymerization reaction has progressed past the liquid
phase and achieved a viscosity of 400, optionally 500 Pascal/second or
lesser or greater or intermediate viscosity. Optionally, exemplary mixing
apparatus according to the present invention may be employed to mix a
liquid mixture by adjusting a distance between the mixing elements.
Optionally, exemplary mixing apparatus according to the present invention
may be employed to mix a cement prepared according to a previously known
formulation after the mixture reaches viscosity of at least 100
Pascal/second.

[0114]FIG. 1 is a simplified flow diagram illustrating sequence of acts
associated with performance of a method 100 according to exemplary
embodiments of the invention.

[0115]At 110 components are placed into a mixing well or mixing well of a
mixing apparatus. Optionally this operation may be performed as part of a
manufacturing procedure of apparatus 200.

[0116]Optionally, one or more wiping elements are deployed 120. Deployment
may be in the mixing well or on a cover and/or on mixing elements of the
mixing apparatus and may occur before or after components are placed 110
in the mixing well.

[0117]At 130 mixing elements are inserted into the mixing well so that
they are at least partially submerged in components of the mixture. If a
wiping element has been deployed 120, the components of the mixture are
generally below the wiping element at this stage.

[0118]A drive mechanism is operated to mix 140 the components. As
described hereinabove, according to exemplary embodiments of the
invention, mixing 140 will cause the components to form a high viscosity
mixture in a relatively short period of time, optionally in a few
seconds. In an exemplary embodiment of the invention, satisfactory
preparation of bone cement is achieved by continuing mixing 140 after the
high viscosity mixture has been formed. Optionally, operation of the
drive mechanism is manual and/or driven by a motor or by compressed air
or by any other external source of force known in the art.

[0119]After mixing 140 is complete, mixing elements 150 are removed. If a
wiping element has been deployed 120, automatic wiping 152 of the mixing
elements occurs at this stage. Optionally, the wiping element remains in
the mixing well during and/or after withdrawal 150.

[0120]Optionally, cement is transferred 160 from the mixing well to an
injection reservoir directly. Optionally, transfer 160 is accomplished
using transfer apparatus which comprises an exemplary embodiment of the
invention.

Exemplary Apparatus

[0121]FIGS. 2, 3, 6, 7 and 8 depict an exemplary embodiment of a mixing
apparatus 200 according to the present invention

[0122]FIG. 2 shows an exemplary apparatus 200 with a cover 220 removed
from a base 250. Cover 220 is depicted with an optional locking ring 224
which mates to a set of threads 256 on base 250.

[0123]In some exemplary embodiments of the invention, components are
placed 110 in a mixing well 252 at this stage.

[0124]In other embodiments of the invention, components are placed 110 in
mixing well 252 as part of a manufacturing and assembly process.
Optionally, apparatus 200 is supplied assembled as depicted in FIG. 3.
When apparatus 200 is supplied assembled with mixture components inside,
undesired premature mixing of monomer liquid and polymer powder may be
prevented by a variety of methods. Exemplary methods of preventing
undesired premature mixing are described below.

[0125]Cover 220 includes portions of a drive mechanism. The drive
mechanism is optionally a manual mechanism operable by a handle 210. In
the pictured embodiment, cover 220 includes a downward facing protrusion
222 (FIG. 6) configured to engage a wiping element 260 by means of
engagement arms 262.

[0127]In another exemplary embodiment, engagement arms 262 A function to
engage protrusion 222 and to engage a groove 264 in base 250. A
relationship between engagement arms 262 A and groove 264 in base 250 is
described below.

[0128]A central mixing element 230 and a planetary mixing element 240 are
visible protruding downwards from cover 220. Optionally, two or more
planetary mixing elements 240 are provided. A portion of a planetary
drive gear 270 is also visible in this view.

[0129]Base 250 includes an inner mixing well 252 and a series of inward
facing teeth which function as a stationary circumferential gear 254.
Stationary circumferential gear 254 is a part of the drive mechanism and
is configured to engage planetary drive gear 270 when cover 220 is
assembled with base 250.

[0132]FIG. 4A is a schematic representation of an exemplary drive
mechanism viewed from above base 250. The physical relationship between
planetary gear 270, planetary drive shaft 272, central mixing element
230, stationary circumferential gear 254 and drive element 232 (pictured
here as a lever) is more clearly visible in this view than in the
preceding figure. Engineering considerations of the drive mechanism are
discussed below. In an exemplary embodiment of the invention, stationary
circumferential gear 254 has 3 times as many teeth as planetary drive
gear 270.

[0133]Mixing elements 230 and 240 are optionally roughened, serrated or
striated to insure formation of a boundary layer in the material being
mixed in proximity to a surface of the mixing elements during mixing.
Optionally, an inner surface of well 252 is similarly roughened, serrated
or striated to insure formation of a boundary layer in proximity to a
surface of the well.

[0134]In an exemplary embodiment of the invention, serrations in the form
of vertical slits that extend along the full height of mixing elements
230 and/or 240. Optionally, the longitudinal slits contribute to easy
introduction and removal of mixing elements 230 and/or 240 through wiping
apertures in wiping element 260. Optionally, vertical slits are
characterized by a depth of 0.1, 0.5 or 1 mm or lesser or greater or
intermediate depths.

Exemplary Drive Mechanism Engineering considerations

[0135]FIG. 4B is an engineering projection showing rotation directions and
distances for an exemplary drive mechanism respectively; The view is
looking down on base 250 as for FIG. 4A.

During operation point "A" on an outer surface of central mixing element
230 will move counterclockwise (arrow) with a radial velocity V (A):

V(A)=ω1*R1

where ω1 is a rotational speed of mixing element 230 in radians/sec
and R1 is the radius of mixing element 230.During operation point "B" on
a surface of planetary mixing element 240 will have a radial velocity
V(B) comprising the sum of velocity due to planetary mixing element 240
rotation relative to the axis of central mixing element 230 and velocity
due to planetary mixing element 240 rotation on its own axis:

V(B)=ω1*R(B)+ω2*R2 [0136]where ω2=i*ω1
[0137]where "i" is the ratio between the number of teeth of the
stationary circumferential gear 254 and the number of teeth on planetary
gear 270; [0138]and ω1 is a rotational speed of mixing element 230;
[0139]R(B) is a distance from a center of mixing element 230 to a closest
point (B) on mixing element 240; and [0140]R2 is the radius of mixing
element 240During operation point "C" on an opposite surface of planetary
mixing element 240 will have a radial velocity V(C) comprising the
difference between velocity due to planetary mixing element 240 rotation
relative to the axis of central mixing element 230 and velocity due to
planetary mixing element 240 rotation on its own axis:

[0140]V(C)=ω1*R(C)-i*ω1*R2 [0141]where R(C) is a distance
from a center of mixing element 230 to a farthest point (C) on mixing
element 240; and [0142]the remaining terms are as defined above.Point D
on stationary circumferential gear 254 will have a velocity of zero.The
shear stresses on a mixture flowing between pints A and B, or between
points C and D, can be calculated by the subtraction of radial velocities
between opposing points (velocity gradients):The shear stresses between
the fixed position and planetary mixing elements correlate to:

[0142]V(B)-V(A)=ω1*(R(B)-R1+iR2)

The shear stresses between the planetary mixing element and to stationary
mixing chamber inner surface correlate to
V(C)-V(D)=ω1*(R(C)-iR2).In an exemplary embodiment of the
invention, apparatus 200 is operated manually, so ω1 is set by the
operator. Optionally, ω1 can be 10, 15, 22, or 30 RPM or lesser or
greater or intermediate values.In an exemplary embodiment of the
invention, R1, R2, R(B), R(C) and i, are selected to meet both geometry
considerations and relatively similar velocity gradients that are
sufficient to produce adequate shear stresses in consideration of a
selected viscosity, such as, for example, 500 Pascal/second.

[0143]FIG. 5 illustrates a theoretic gradient of the shear stress applied
to a mixture 500 flowing between a two elements (e.g. planetary mixing
element 240 and central mixing element 230 or planetary mixing element
240 and an inner wall of mixing well 254). As the viscosity of mixture
500 increases, the shear stress necessary for mixing also increases.

[0144]In an exemplary embodiment of the invention, sufficient shear force
to mix a mixture 500 characterized by a viscosity of 500 Pascal/second is
provided by adjusting distance between the two mixing elements (A to B in
FIG. 4B) or between planetary mixing element 240 and an inner wall of
mixing well 254 (C to D in FIG. 4B) to 1 to 5 mm, optionally about 2 mm.
Alternatively or additionally, shear force may be adjusted by varying the
surface area of mixing elements 230 and/or 240 and/or an inner surface of
well 252 which contacts the mixture.

Wiping Element

[0145]FIGS. 6, 7 and 8 illustrate placement and function of optional
wiping element 260 according to an exemplary embodiment of the invention.

[0147]FIG. 7 illustrates cover 220 assembled on base 250 so that wiping
elements 230 and 240 are in close proximity to floor 258 of mixing well
252. Engagement arms 262 of wiping element 260 are seated in groove 264
of mixing well 252 (magnified in inset for clarity). Each of engagement
arms 262 slides circumferentially around mixing well 252 in groove 264 as
planetary mixing element 240 travels around mixing well 252.

[0148]FIG. 8 illustrates removal 150 of mixing elements 230 and 240 from
mixing well 252. Engagement arms 262 are retained by groove 264 so that
wiping element is locked into position. Removal of elements 230 and 240
results in automatic wiping 152 by the edges of the wiping apertures.

Transfer Mechanism;

[0149]FIGS. 9 and 10 illustrate a transfer mechanism according to
exemplary embodiments of the invention as previously disclosed in
co-pending U.S. application Ser. No. 11/360,251, the disclosure of which
is fully incorporated herein by reference. FIG. 9 is a cross-sectional
view and FIG. 10 is a partial cut-away view in perspective.

[0151]In the pictured embodiment transfer piston cup 950 is fitted with a
second set of threads 952 which engage matching threads 930 on injection
reservoir 910. In operation injection reservoir 910 is attached to
transfer piston cup 950 by threads 930 and 952 before transfer piston cup
950 is inserted into mixing well 252. As transfer piston cup 950 descends
into mixing well 252, contents of mixing well 252 (e.g. high viscosity
bone cement) are forced upwards into injection reservoir 910. Injection
nozzle 920 serves to release air from injection reservoir 910 so that no
resistive pressure accumulates. The mixed material has been transferred
160 to the injector at this stage. Optionally, an operator of the
apparatus knows that reservoir 910 is full when bone cement exits
injection nozzle 920.

Exemplary Dimensions

[0152]According to various exemplary embodiments of the invention, an
inner volume of the mixing well 252 is 5, optionally 10, optionally 20,
optionally 40, optionally 60, optionally 80, optionally 100 ml or lesser
or greater or intermediate volumes. In an exemplary embodiment of the
invention, the mixing well volume is 50 to 60 ml, optionally about 66 ml,
and 10 to 20 ml of mixture, optionally about 15 ml of mixture is placed
in the chamber for mixing. In an exemplary embodiment of the invention, a
portion of the inner volume of well 252 is occupied by mixing elements
230 and 240.

[0153]Optionally, an inner diameter of the mixing well is 20, optionally
40, optionally 60, optionally 80, optionally 100 mm or lesser or greater
or intermediate sizes. In an exemplary embodiment of the invention, the
inner diameter of the mixing well is 40 to 50 mm, optionally about 46 mm.

[0154]Optionally, a height of the mixing well is 20, although it can be
40, 60, 80, or 100 mm or lesser or greater or intermediate sizes. In an
exemplary embodiment of the invention, the height of the mixing well is
35 to 45 mm, optionally about 40 mm.

[0155]Optionally, an aspect ratio (diameter/height) of the mixing well is
0.7, 0.9, 1.1, or 1.3, or lesser or greater or intermediate values. In an
exemplary embodiment of the invention, aspect ratio (diameter/height) of
the mixing well is 1.1 to 1.2, optionally about 1.15.

[0156]In an exemplary embodiment of the invention, a distance (d1)
between the central mixing element and the planetary mixing element
(indicated by A to B in FIG. 4A) and/or a distance (d2) between the
planetary mixing element and an inner wall of the mixing well (indicated
by C to D in FIG. 4A) is 1, 2, 3, 4, or 5 mm or lesser or greater or
intermediate distances. In an exemplary embodiment of the invention,
d1 is substantially equivalent to d2.

[0157]In typical vertebrae treatment procedures, a volume of approximately
5 ml is injected in a single vertebra. It is common to prepare a batch of
approximately 8 ml of cement if a single vertebra is to be injected,
approximately 15 ml of cement if two vertebrae are to be injected and
progressively larger volumes if three or more vertebrae are to be
injected. Combination of powdered polymer component and liquid monomer
component leads to a reduction in total mixture volume as the polymer is
wetted by the monomer. For example, 40 to 50 ml of polymer powder may be
mixed 112 with 7 to 9 ml of monomer liquid to produce 18 ml of
polymerized cement. In an exemplary embodiment of the invention, a volume
of well 252 is selected to accommodate the large initial column of
monomer powder, even when a significantly smaller batch of cement is
being prepared.

[0158]In an exemplary embodiment of the invention, a dead volume of cement
remaining in well 242 after transfer to injection reservoir 910 by
transfer element 900 is less than 2, 1, or 0.5 ml or lesser or
intermediate values.

[0159]In an exemplary embodiment of the invention, a diameter of central
mixing element 230 and a diameter of injection reservoir 910 are both
equivalent to a diameter of an aperture in wiping element 260.
Optionally, this conformity of diameters reduces a dead volume of cement
left in well 252 after operation of transfer apparatus 900. Optionally
the diameters are all approximately 18 mm.

[0160]In other embodiments of the invention (not shown), mixing well 252
of base 250 is transferred to an injection apparatus and cement is
injected into a subject directly from well 252. Optionally, this occurs
after removal of mixing elements 230 and 240.

Exemplary Materials

[0161]In an exemplary embodiment of the invention, component parts of the
mixing apparatus are constructed of Polyamides (e.g., Nylon) and/or
Polypropylene.

[0162]Optionally, some portions of the apparatus are constructed of a
metal, for example stainless steel. In an exemplary embodiment of the
invention, metal is employed to construct parts which are subject to
large forces, such as friction or torque. Optionally, one or more of
handle 210, gears (e.g. 270), teeth (e.g. 254), drive arms (e.g. 232) and
mixing elements (e.g. 230 and/or 240) are constructed of metal.

Exemplary Methods of Use

[0163]In an exemplary embodiment of the invention, apparatus 200 is
provided with instructions for use. In an exemplary embodiment of the
invention, the instructions indicate a procedure for achieving complete
mixing of a mixture placed in well 252.

[0164]Optionally, these instructions indicate an amount of time
recommended to insure complete mixing. In an exemplary embodiment of the
invention, the time is 30 to 90 seconds, optionally 30 to 60 seconds,
optionally about 45 seconds or lesser or greater or intermediate amounts
of time.

[0165]Optionally, these instructions indicate a number of turns
recommended to insure complete mixing. In an exemplary embodiment of the
invention, the number of turns is 20 to 100, optionally 40 to 60,
optionally about 50 or a lesser or greater or intermediate number.

[0166]Optionally, these instructions indicate a signal which will be
presented to the user when mixing is complete. The signal may be a visual
signal (e.g. indicator light) or an audible signal (e.g. buzzer or bell)
or a tactile signal (e.g. gear 270 slips on teeth 254 when a desired
viscosity is reached). In an exemplary embodiment of the invention, the
signal is triggered by a closed feedback loop. The loop may rely upon,
for example, an indirect measure of viscosity (e.g. torque), centripetal
force, time, number of revolutions of a portion of apparatus 200 (e.g.
handle 210, gear 270 or mixing element 230 and/or 240) or mixture volume.

[0167]Optionally, the apparatus combines a mechanism that allow turning of
handle only during a preset window of time and/or number of rotations.

Shear Force Considerations

[0168]Shear force on a mixture within well 252 is affected primarily by
surface properties, distance between surfaces, and differences in
velocities between surfaces.

[0169]Surface properties of mixing elements 230, 240 and an inner surface
of well 252 all affect applied shear forces on mixture 500 (FIG. 5).
Increasing roughness (e.g. by serration or striation) prevents mixture
500 from slipping against these surfaces by increasing the force of
friction. When the surfaces are sufficiently roughened, a boundary layer
will have a relative velocity of zero with respect to the surface.
Optionally, this zero relative velocity contributes to increased shear
force.

[0170]Distances between surfaces are inversely related to shear forces
acting on a mixture 500 moving between the surfaces. In an exemplary
embodiment of the invention, as distances defined by lines A-B and/or C-D
(FIG. 4B) increase, an applied shear force to a portion of mixture 500
crossing those lines decreases.

[0171]Differences in relative velocities between portions of mixer 200
also affect shear forces on mixture 200. As the difference in relative
velocities increases, the applied shear force to a portion of mixture 500
flowing between the elements increases. The relative velocities are
optionally influenced by angular velocities and/or radial velocities
and/or radius of the elements involved as discussed in more detail above.
In an exemplary embodiment of the invention, differences in relative
velocity are amplified by imparting angular velocities with different
directions to mixing elements 240 and 230.

General

[0172]Because some components of a bone cement mixture may have an
unpleasant odor and/or be toxic if inhaled, some exemplary embodiments of
the invention include safety features to reduce exposure to undesired
vapors.

[0173]In an exemplary embodiment of the invention, locking ring 224 is
equipped with an air-tight seal (e.g. rubber or silicon) which prevents
vapors from escaping from well 252.

[0174]Alternatively or additionally, apparatus 200 may be provided with an
evacuation port (not shown) connectable to a vacuum source. In an
exemplary embodiment of the invention, the vacuum source is a standard
"wall suction" unit in a hospital operating room and the undesired vapors
are from an MMA component of a bone cement mixture.

[0175]In cases where apparatus 200 is supplied with components to be mixed
inside well 252, a method for preventing undesired premature mixing may
be implemented.

[0176]One exemplary method of preventing undesired premature mixing of
monomer liquid and polymer powder is to provide the monomer liquid in a
sealed bag or capsule which is burst when apparatus 200 is operated. The
capsule may be burst when it is drawn across line A-B or C-D by the flow
of mixture 500. In an exemplary embodiment of the invention, the capsule
is designed so that it is characterized by a smallest dimension which
exceeds the length of A-B and/or C-D. In an exemplary embodiment of the
invention, the bag or capsule is constructed of a biocompatible material
which may be injected together with the bone cement.

[0178]Another exemplary method of preventing undesired premature mixing of
monomer liquid and polymer powder is to provide the monomer liquid in a
cavity inside a wall of mixing well 252. Optionally, contents of the
cavity are dumped into well 252 manually or automatically when mixing
commences.

[0179]The present invention has been described using detailed descriptions
of embodiments thereof that are provided by way of example and are not
intended to necessarily limit the scope of the invention. In particular,
numerical values may be higher or lower than ranges of numbers set forth
above and still be within the scope of the invention. The described
embodiments comprise different features, not all of which are required in
all embodiments of the invention. Some embodiments of the invention
utilize only some of the features or possible combinations of the
features. Alternatively or additionally, portions of the invention
described/depicted as a single unit may reside in two or more separate
physical entities which act in concert to perform the described/depicted
function. Alternatively or additionally, portions of the invention
described/depicted as two or more separate physical entities may be
integrated into a single physical entity to perform the
described/depicted function. Variations of embodiments of the present
invention that are described and embodiments of the present invention
comprising different combinations of features noted in the described
embodiments can be combined in all possible combinations including, but
not limited to use of features described in the context of one embodiment
in the context of any other embodiment. The scope of the invention is
limited only by the following claims.

[0180]In the description and claims of the present application, each of
the verbs "comprise", "include" and "have" as well as any conjugates
thereof, are used to indicate that the object or objects of the verb are
not necessarily a complete listing of members, components, elements or
parts of the subject or subjects of the verb.

[0181]All publications and/or patents and/or product descriptions cited in
this document are fully incorporated herein by reference to the same
extent as if each had been individually incorporated herein by reference.